Techniques for automatic gain control in a frequency domain for a signal path for a frequency modulated continuous wave (FMCW) light detection and ranging (LIDAR) system

ABSTRACT

A light detection and ranging (LIDAR) system includes an automatic gain control (AGC) unit to reduce the dynamic range, reducing processing power and saving circuit area and cost. The system detects a return beam of a light signal transmitted to a target, having a first dynamic range in a time domain. An analog to digital converter (ADC) generates a digital signal based on the return beam. A processor can perform time domain processing on the digital signal, convert the digital signal from the time domain to a frequency domain, and perform frequency domain processing on the digital signal in the frequency domain. The AGC unit can measure a power of the return beam, and apply variable gain in the frequency domain to reduce a dynamic range of the return beam to a second dynamic range lower than the first dynamic range.

RELATED APPLICATIONS

This application is a nonprovisional application based on, and claimspriority to, U.S. Provisional Application No. 63/220,280 filed Jul. 9,2021. That provisional application is incorporated herein by reference.

This application is related to U.S. patent application Ser. No.17/675,857, titled: TECHNIQUES FOR AUTOMATIC GAIN CONTROL IN A TIMEDOMAIN FOR A SIGNAL PATH FOR A FREQUENCY MODULATED CONTINUOUS WAVE(FMCW) LIGHT DETECTION AND RANGING (LIDAR) SYSTEM, filed concurrentlyherewith.

FIELD

Descriptions are generally related to light scanning systems, and moreparticularly, LIDAR (light detection and ranging) systems.

BACKGROUND

The dynamic range of a frequency modulation continuous wave (FMCW) lightdetection and ranging (LIDAR) system is the difference between thehighest intensity signal and lowest intensity signal received that canbe reliably processed. Signals with intensities that are too high canget distorted, which can introduce harmonics and make it difficult forthe system to reliably pick the true frequency peak. Signals withintensities that are too low can become indistinguishable from noisesources, which makes the signals difficult to detect.

The dynamic range of an FMCW LIDAR system can be limited by the minimumdynamic range of any individual component in the optical, electrical,and signal processing paths. A system can add bits to analog to digitalconverters (ADCs) and digital datapaths, which lowers the quantizationnoise level, and can increase the dynamic range. However, adding bitsincreases the power, area, and cost of the LIDAR system. Additionally,adding bits may not increase the dynamic range if optical or analogcomponents limit the dynamic range.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description includes discussion of figures havingillustrations given by way of example of an implementation. The drawingsshould be understood by way of example, and not by way of limitation. Asused herein, references to one or more examples are to be understood asdescribing a particular feature, structure, or characteristic includedin at least one implementation of the invention. Phrases such as “in oneexample” or “in an alternative example” appearing herein provideexamples of implementations of the invention, and do not necessarily allrefer to the same implementation. However, they are also not necessarilymutually exclusive.

FIG. 1 illustrates an example of automatic gain control (AGC) fordynamic range control in a LIDAR system.

FIG. 2 illustrates an example of a LIDAR system that provides AGC foroptical signal processing.

FIG. 3 illustrates an example of AGC in an LO path of a LIDAR system.

FIG. 4 illustrates an example of AGC in an analog processing path of aLIDAR system.

FIG. 5 illustrates an example of AGC in time domain digital processingof a LIDAR system.

FIG. 6 illustrates an example of digital time domain AGC operation.

FIG. 7 illustrates an example of AGC in frequency domain digitalprocessing of a LIDAR system.

FIG. 8 illustrates an example of digital frequency domain AGC operation.

FIG. 9 illustrates an example of digital frequency domain AGC operationin multiple frequency bands.

FIG. 10 illustrates an example LIDAR system that can implement AGC.

FIG. 11 represents a time-frequency diagram illustrating an example ofLIDAR waveform detection and processing.

FIG. 12 illustrates an example of a LIDAR system that provides AGC for aLIDAR signal.

Descriptions of certain details and implementations follow, includingnon-limiting descriptions of the figures, which may depict some or allexamples, and well as other potential implementations.

DETAILED DESCRIPTION

As described herein, in accordance with embodiments of the presentinvention, a light detection and ranging (LIDAR) system can includeautomatic gain control (AGC). According to some embodiments, AGCsdescribed herein can include one or more signal processors includedtherein or remotely and/or one or more measuring components. The AGC canadjust the dynamic range of a system while maintaining approximately thesame power, area, and cost as a traditional system. One example systemis a frequency modulated continuous wave (FMCW) LIDAR system, where thedynamic range of the system is improved by one or more variable gaincontrol elements. The dynamic range of an FMCW LIDAR system can bedefined as the difference between the highest intensity and lowestintensity received signal or beat signal that can be reliably processed.

The AGC can control the dynamic range of the system across optical,analog or electrical, or digital paths of the signaling, or acombination of optical, electrical, and digital paths. The AGC providesdynamic range control to reduce signal distortion due to a dynamic rangethat is too high, and reduce noise interference in peak detection due todynamic range that is too low.

In one example, AGC can be provided in an optical path. In one example,AGC can be provided in analog or electrical circuitry. In one example,AGC can be provided in digital time domain processing. In one example,AGC is provided in digital frequency domain processing. AGC can beapplied in a combination of one or more of the optical circuitry, analogcircuitry, digital time domain processing, or digital frequency domainprocessing.

The system can detect a return beam of a light signal transmitted to atarget, having a first dynamic range in a time domain. An analog todigital converter (ADC) can generate a digital signal based on thereturn beam. A processor can perform time domain processing on thedigital signal, convert the digital signal from the time domain to afrequency domain, and perform frequency domain processing on the digitalsignal in the frequency domain. The AGC unit can measure a power of thereturn beam, and apply variable gain in the time domain to reduce adynamic range of the return beam to a second dynamic range lower thanthe first dynamic range. The AGC unit can measure a power of the digitalsignal, and apply variable gain in the frequency domain to reduce adynamic range of the signal to a second dynamic range lower than thefirst dynamic range.

FIG. 1 illustrates an example of automatic gain control (AGC) fordynamic range control in a LIDAR system. System 100 represents anadjustment to dynamic range based on AGC.

Dynamic range refers to a difference between the largest possible signalpower and the smallest possible signal power that needs to be reliablyprocessed. Dynamic range can be a design specification for a LIDARsystem, and can be based on the expected signals used, power budget forthe system, component performance characteristics, or other factors.Performing signal processing on signals with lower dynamic range cansave power, reduce optical component size, thus saving area, and canreduce the system cost (both component cost and operating cost). TheLIDAR system can be designed with a datapath having a smaller dynamicrange than what is specified for the components. The system can measurethe power of a received signal and apply a variable gain to fit thesignal within the reduced dynamic range for processing through thedatapath.

A variable gain can be applied to any signal to reduce its dynamicrange. Variable gain can be applied to gain up weak signals. Variablegain can be applied to attenuate strong signals. Either amplification,or attenuation, or both amplification and attenuation can be applied toadjust the dynamic range.

By applying the variable gain, a signal can be made to fit within thedynamic range of the next component in the signal chain or along thedatapath. Thus, the variable gain AGC can be applied to fit dynamicrange above the noise level and below the distortion level of acomponent. It will be understood that applying variable gain at a pointin the path of the signal, whether in the optical, analog, or digitaldomain, will adjust the dynamic range for subsequent components in thesignal path. Thus, applying a variable gain can reduce the dynamic rangerequirement of all subsequent signal chain components, resulting inpower, area, and cost savings. The earlier AGC is applied in a signalchain, the more savings are possible.

In system 100, the difference between signal 112 with large amplitudeand signal 114 with very small amplitude can be high dynamic range 110.System 100 can apply variable gain to achieve low dynamic range 140. Todetermine the optimal variable gain to apply, system 100 can measure theinput signal level, as represented by device 122, which represents ameasuring device or measuring apparatus of system 100 to generatemeasurement signal 124. AGC 120 represents one or more AGC circuits toapply the variable gain.

AGC 120 can receive signal 124 to indicate the measurement of the inputsignal, determine the desired signal levels to be within a desireddynamic range, and generate control signal 126 to apply variable gain.Control signal 126 can set one or more configuration parameters ofvariable gain 130 to apply the desired variable gain. The input signallevel could be an average level over time or frequency or a peak level,such as instantaneous peak voltage or light intensity or peak frequencycomponent. Variable gain 130 represents one or more components to applyvariable gain to one or more signals to produce low dynamic range 140.In system 100, the result of the application of variable gain 130 can bethat the high amplitude of signal 112 has been attenuated to signal 142with lower amplitude, and the low amplitude of signal 114 has beengained or amplified to signal 144 with higher amplitude.

In one example, either signal 112 or signal 114 are adjusted by variablegain 130, but not both. For example, signal 112 can be attenuated andsignal 114 can remain unchanged. Alternatively, signal 112 can remainunchanged while signal 114 is gained. The determination to gain orattenuate a signal is made based on the desired lower dynamic range.

Automatic gain control can refer to measuring the input signal level,computing the variable gain or gain range to apply, and controlling thevariable gain component. Such operation can minimize the requireddynamic range, which also reduces power consumption, circuit area, andcost of the rest of the signal path.

FIG. 2 illustrates an example of a LIDAR system that can provide AGC foroptical signal processing. System 200 provides an example of a LIDARsystem. Laser 210 represents a laser transmission system or opticalsource or light source that provides a light signal or optical sourcefor scanning the target. In some implementations, laser 210 representsan FMCW laser. Optical components 220 provide the modulation and opticsto transmit TX signal 212 to target 230 and receive the reflectionsignal represented by RX signal 232.

Photodetector 240 can receive RX signal 232 from optical components 220from target 230, and LO signal 214 from optical components 220 fromlaser 210. LO signal 214 represents a reference signal generated fromthe laser light signal. LO signal can represent transmission of a firstportion of a light signal from laser 210 toward target 230.Photodetector 240 detects a return beam from target 230, where thereturn beam is the light signal of TX signal 212 as reflected back fromtarget 230.

System 200 can condition the signal (e.g., the return beam) with ADC 250and provide the conditioned signal for digital signal processing 260. Inone example, digital signal processing 260 generates point cloud 262,which can represent a group of points of estimates of targetinformation. A point cloud can refer to a group of target estimatevalues that have corresponding coordinate information to spatially mapthe points relative to each other.

The digital signal processing can include frontend processing 270, withtime domain processing of the input samples, block samples for frequencytransformation (FT), and frequency domain processing. Time domainprocessing 272 can apply time domain filters to improve SNR of thesignal. Time domain processing 272 has input samples 264 as the input,which represent samples generated by ADC 250.

Block samples for FT (Fourier Transform) 274 represents processing onthe samples to group them for frequency transformation computations.Time to frequency (FRED) domain 276 represents the frequencytransformation to provide a conversion of the signals into temporalfrequency representations. Frontend processing 270 can include frequencydomain processing 278 to generate a filtered frequency domain waveform282. Frequency domain processing 278 can perform processing on thedigital signal in the frequency domain.

Digital signal processing 260 can include peak search 280 of frequencydomain waveform 282 to generate signal detections 284 or computations ofestimates of the points of interest. The points of interest generatedcan be represented as a point cloud, with point having range andvelocity information, associated in a relative spatial mapping.

Along various signal paths of system 200, the components can be designedor configured with a dynamic range for operation. In one example, system200 applies AGC to adjust the dynamic range of the signal for subsequentcomponents in the signal path. In one example, the AGC measures a powerof a signal in the time domain and applies variable gain in the timedomain to reduce a dynamic range of the signal to prepare the signal forsubsequent components.

There are many possible locations for the application of AGC in system200. In one example, system 200 can include optical AGC, applying avariable gain to LO signal 214 prior to photodetector 240. In oneexample, system 200 can include analog AGC, applying a variable gain toan analog or electrical signal prior to ADC 250. In one example, system200 can include digital time domain AGC, applying variable gain to adigital signal prior to frequency domain conversion. In one example,system 200 can include digital frequency domain AGC, applying variablegain to a digital signal after frequency domain conversion. In the caseof digital frequency domain AGC, different frequency bands could havedifferent gains applied for further expansion of dynamic range. Itshould be noted that one or more AGCs described in the presentdisclosure can be used in combination to achieve advantages describedherein.

In one example, system 200 applies AGC only at one of the identifiedlocations. In an alternative example, system 200 can apply AGC atmultiple locations. In some scenarios, the application of AGC atmultiple locations would have benefit if the signal level changesnaturally between the previous AGC location and the next, rather than achange due to the application of AGC. Thus, a signal level change due tocomponents or processing can be adjusted by the application of anotherlevel of AGC. If there is no natural change in signal level between theLO, ADC, and time domain processing (which could be the case for anexample of system 200), system 200 could apply AGC at only one of thoselocations. Signals in the same frequency range that have not beenfiltered would not normally see a signal level change. Thus, in typicalsystems, AGC can be applied at optical, analog, or digital time domainprocessing. Even with application of AGC at one of these locations, theapplication of digital frequency domain processing can still bebeneficial.

In some scenarios, one or more AGCs can be placed in desirable locationswithin a given system (e.g., in the signal chain or signal path) basedon the costs and benefits to the system. Location 292, location, 294,location 296, and location 298 represent locations in system 200 wherean AGC can be employed. Location 292 represents an optical AGC in theoptical path. Location 294 represents an electrical AGC in the analogprocessing path. Location 296 represents a digital processing AGC in thetime domain processing path. Location 298 represents a digitalprocessing AGC in the frequency domain processing path.

AGC in the digital frequency domain can be applied to a filtered band offrequencies. There can be benefits to system 200 by applying digitalfrequency domain AGC in conjunction with optical, analog, or digitaltime domain AGC for additional power savings.

FIG. 3 illustrates an example of AGC in an LO path of a LIDAR system.System 300 represents a system in accordance with embodiments of thepresent disclosure. System 300 provides an example of a LIDAR system.Laser 310 represents a laser transmission system that provides a lightsignal or optical source for scanning the target. In someimplementations, laser 310 represents an FMCW laser. Optical components320 provide the modulation and optics to transmit TX signal 312 totarget 330 and receive the reflection signal or return beam representedby RX signal 332.

Photodetector 340 can receive RX signal 332 from optical components 320from target 330, and LO signal 314 from optical components 320 fromlaser 310. Photodetector 340 detects the return beam from target 330.System 300 can condition the signal (e.g., the return beam) with ADC 350and provide the conditioned signal for signal processing.

In one example, system 300 includes an optical AGC 360, which controlsvariable gain of LO signal 314 in the time domain based on measurementof RX signal 332. In system 300, optical AGC 360 can measure RX signal332 to determine the signal power and determine whether the dynamicrange will be within specifications for subsequent components. OpticalAGC 360 can control variable gain 362 in the LO path to adjust the beatsignal power as needed.

In one example, an attenuated version of the transmit signal can bemixed with the signal received from the target to obtain a beat signal.Beat signal 342 is illustrated as an output of photodetector 340.Photodetector 340 can receive LO signal 314 and RX signal 332. The morepower incident on photodetector 340, the more power it consumes. System300 can control the LO power. The power consumed by photodetector 340gives an estimate of the power of the received signal (RX signal 332).

When power consumption of photodetector 340 increases, optical AGC 360can decrease the power of LO signal 314 with an optical attenuator tokeep the overall power consumption constant and ensure the power of beatsignal 342 is within the dynamic range of ADC 350. If LO signal 314needs to be gained up, system 300 can use an optical amplifier in the LOpath or adjust the split ratio while generating LO signal 314 fromtransmit signal 312.

Optical components 320 can include a splitter (not specificallyillustrated) to separate TX signal 312 as a first portion of the lightsignal generated by laser 310 and a LO signal 314 as a second portion ofthe light signal. In one example, optical AGC 360 measures RX signal 332for comparison against a threshold (e.g., the comparison performed by asignal processor or similar processor described herein). If thethreshold is determined to be exceeded, optical AGC 360 can attenuate LOsignal 314 with an optical attenuator; thus, variable gain 362 canrepresent an optical attenuator. If the threshold is determined to notbe exceeded, optical AGC 360 can increase the variable gain.

In one example, optical AGC 360 compares RX signal 332 against multiplethresholds. Based on the comparison of RX signal 332 against themultiple thresholds, optical AGC 360 can turn one or more opticalattenuators off; thus, variable gain 362 can represent multiple opticalattenuators controlled based on multiple threshold levels.

In one example, optical AGC 360 measures RX signal 332 for comparisonagainst a threshold, and if the threshold is determined to not beexceeded, optical AGC 360 can increase an amount of TX signal 312relative to LO signal 314, for example, by adjustment to gain orattenuation of a splitter in optical components 320.

FIG. 4 illustrates an example of AGC in an analog processing path of aLIDAR system. System 400 represents a system in accordance withembodiments of the present disclosure. System 400 provides an example ofa LIDAR system. Laser 410 represents a laser transmission system thatprovides a light signal or optical source for scanning the target. Insome implementations, laser 410 represents an FMCW laser. Opticalcomponents 420 provide the modulation and optics to transmit TX signal412 to target 430 and receive the reflection signal or return beamrepresented by RX signal 432. Optical components can include a splitterto separate LO signal 414 from TX signal 412.

Photodetector 440 can receive RX signal 432 from optical components 420from target 430, and LO signal 414 from optical components 420 fromlaser 410. Photodetector 440 detects the return beam from target 430.System 400 can condition the signal (e.g., the return beam) with ADC 450and provide the conditioned signal for signal processing. In oneexample, RX signal 432 can be mixed with LO signal 414 to obtain a beatsignal. Beat signal 442 is illustrated as an output of photodetector440.

In one example, system 400 includes analog AGC 460, which represents ananalog or electrical AGC. In system 400, analog AGC 460 can measure beatsignal 442 generated by photodetector 440 to determine average power orpeak instantaneous voltage. The measurement enables analog AGC 460 todetermine the amount of variable gain 462 needed to ensure the resultingsignal lies within the dynamic range of ADC 450. The application ofvariable gain 462 resulting from analog AGC 460 can enable the use ofADC 450 in system 400 with fewer output bits, or lower full-scalevoltage, or a combination of lower voltage and fewer output bits. Usingfewer bits or lower voltages can save power, area, and cost as comparedto a system that does not use AGC in the manner described herein.

In one example, system 400 includes additional analog circuitry tomeasure the input signal level, such as an envelope detector. System 400can provide variable gain 462 with, for example, a variable gainamplifier or other electronic circuit.

FIG. 5 illustrates an example of AGC in time domain digital processingof a LIDAR system. System 500 represents a system in accordance withembodiments of the present disclosure. System 500 does not illustratethe optical components.

System 500 can detect a return beam signal with photodetector 510 andcondition the signal with ADC 520. System 500 provides the conditionedsignal for signal processing by frontend processing 530. In one example,frontend processing 530 includes time domain processing 532, time tofrequency (FREQ) domain 534, and frequency (FREQ) domain processing 536.Time domain processing 532 can perform time domain filtering of theinput signal.

Time to frequency domain 534 represents a frequency transformation toprovide a conversion of the signal into a temporal frequencyrepresentation. Frequency domain processing 536 can perform processingor filtering on the digital signal in the frequency domain to generate afrequency domain waveform 542. System 500 can include peak search 540 offrequency domain waveform 542 to generate signal detections 544 orcomputations of estimates of the points of interest, such as a pointcloud.

In one example, system 500 includes digital time domain AGC 550 prior totime domain processing 532. Digital time domain AGC 550 can measure theoutput signal level of ADC 520 and adjust the signal (e.g., gain thesignal or reduce the signal power) prior to further processing. Digitaltime domain AGC 550 can control variable gain 552 to adjust the signallevels.

After application of variable gain 552 provided by digital time domainAGC 550, system 500 can use fewer data path bits in the signalprocessing components of frontend processing 530, which saves power,area, and costs. Each downstream component (time domain processing 532,time to frequency domain 534, and frequency domain processing 536) canuse fewer bits as compared to a traditional system that does not useAGC.

In one example, system 500 can perform a power measurement of the inputsignal level from ADC 520 to frontend processing 530 such as a sum ofsquares of input data or simply measuring peak instantaneous input(e.g., max of input data) over a window of samples. In one example,system 500 can apply variable gain 552 by choosing a subset ofcontiguous bits to forward to the rest of the signal chain (thedownstream processing components). Thus, certain bits can be selectedfor processing, and other bits will be ignored for the processing. Inone example, system 500 performs scaling and/or rounding prior toselecting the bits for processing.

In one example, digital time domain AGC 550 compares the digital signallevel to a threshold and adjusts the digital signal with digitalmultiplication, provided the digital signal is not above the threshold.In one example, the threshold can be multiple thresholds, with differentlevels of multiplication applied based on different thresholds.

FIG. 6 illustrates an example of digital time domain AGC operation.System 600 illustrates bits selection in accordance with an example ofsystem 500. The simplest implementation of digital AGC, whether in thetime domain or the frequency domain, is for the processing component(s)to choose a subset of the bits, and only perform processing on thesubset of bits. The subset of bits selected should most accuratelyrepresent the input signal. Thus, the subset selected should be thesubset with the most signal information.

Graph 610 illustrates two signals, input signal A and input signal B.Graph 610 represents the range of distortion at the top (the top grayarea), and the quantization noise and overall noise floor on the bottom(the bottom gray area). The dynamic range is the range between thedistortion and the overall noise floor. Graph 610 also illustrates AGCthreshold 612, assuming two different levels of bit selection. As seento the right of the graph, the signal in the example has 6 bits.

Input signal A has a signal level that is much higher than the noisefloor and could potentially be close to the distortion level. Inputsignal A exceeds AGC threshold 612. In one example, the system selectsthe 4 MSBs (AGC Level 1) out of the 6 available bits. For signals withhigh input level, the MSBs can be chosen to reduce the chance ofdistortion.

Input signal B has a signal level that is lower than AGC threshold 612,and is relatively close to the noise floor. Thus, choosing the 4 MSBswould bury the signal in the noise. The processing component(s) ofsystem 600 can select the 4 LSBs (AGC Level 2) for processing of inputsignal B.

It will be understood that 6 signal bits are illustrated in system 600,and a different system can have more or fewer bits. More or fewer thanthe 4 bits of the example can be selected for processing. In oneexample, the AGC can include more than two levels. For example, system600 could include a second AGC threshold, creating a third AGC level. Athird AGC level could allow selection of the 4 middle bits. More levelsof AGC bit selection would generally have more associated AGCthresholds.

Graph 620 illustrates the processing of input signal A, with a new noisefloor (bottom gray area) and distortion range (top gray area). Thus,graph 620 has a different dynamic range for the 4-bit signal as comparedto the dynamic range of graph 610 for the 6-bit signal. Likewise, ingraph 630, the processing of input signal B illustrates the noise floor(bottom gray area) with a new distortion level (top gray area) anddifferent dynamic range for the 4-bit signal.

System 600 illustrates selecting a subset of contiguous bits to carryforward to the rest of the data path, which allows shrinking the dynamicrange in steps of 6 dB per bit omitted. In one example, system 600 canperform a digital multiplication (scaling) operation prior to bitselection to achieve less than a 6 dB dynamic range reduction. In oneexample, system 600 can perform rounding before discarding LSBs.

FIG. 7 illustrates an example of AGC in frequency domain digitalprocessing of a LIDAR system. System 700 represents a system inaccordance with embodiments of the present disclosure. System 700 doesnot illustrate the optical components.

System 700 can detect a return beam signal with photodetector 710 andcondition the signal with ADC 720. System 700 provides the conditionedsignal for signal processing by frontend processing 730. In one example,frontend processing 730 includes time domain processing 732, time tofrequency (FREQ) domain 734, and frequency (FREQ) domain processing 736.Time domain processing 732 can perform time domain filtering of theinput signal.

Time to frequency domain 734 represents a frequency transformation toprovide a conversion of the signal into a temporal frequencyrepresentation. Frequency domain processing 736 can perform processingor filtering on the digital signal in the frequency domain to generate afrequency domain waveform 742. System 700 can include peak search 740 offrequency domain waveform 742 to generate signal detections 744 orcomputations of estimates of the points of interest, such as a pointcloud.

In one example, system 700 includes digital frequency domain AGC 750prior to frequency domain processing 736, after the conversion of thetime domain signal to the frequency domain. After the signal isconverted to the frequency domain, frequency domain AGC 750 can measurethe signal and apply variable gain 752 based on the signal measurement,to reduce the dynamic range for frequency domain processing. In oneexample, system 700 can divide the signal into multiple frequency bands,with the signal level in each band measured separately. In one example,a different variable gain can be applied to each band. The number offrequency bands and band boundaries can be decided a-priori ordynamically.

The digital implementation of the digital frequency domain AGC can bethe same as the digital time domain AGC described with respect to system500 and system 600. In one example, digital frequency domain AGC 750compares the digital signal level to a threshold and adjusts the digitalsignal with digital multiplication, provided the digital signal is notabove the threshold. In one example, the threshold can be multiplethresholds, with different levels of multiplication applied based ondifferent thresholds.

FIG. 8 illustrates an example of digital frequency domain AGC operation.Diagram 800 illustrates signal processing with digital frequency domainAGC in accordance with an example of system 700.

In diagram 800, the signal for Target 1 is in Band 1, and Gain 1 isapplied to the signal for processing. The signal for Target 2 is in Band2, and Gain 2 is applied to the signal for processing. Gain 1 and Gain 2can be different levels of gain. Such an AGC can preserve a largedynamic range over the full frequency band, while saving power bysignificantly limiting the dynamic range in a single band.

It will be understood that 2 targets with large differences in intensitywithin a single frequency band could generally not be simultaneouslydetected. Signals for targets in different bands can be detected, evenwith large differences in signal intensity.

FIG. 9 illustrates an example of digital frequency domain AGC operationin multiple frequency bands. System 900 illustrates multi-band signalprocessing with digital frequency domain AGC in accordance with anexample of system 700. System 900 illustrates digital frequency domainAGC and variable gain as part of the digital frequency processing.

System 900 illustrates time to frequency conversion, followed by fullband DSP (digital signal processing) 922. Time to frequency conversion(time to FREQ) 910 represents a digital processing component to performa frequency conversion on a time domain digital signal. Frequency domainprocessing 920 represents digital processing in the frequency domain ofthe signal output of time to frequency conversion 910. Frequency domainprocessing 920 includes full band DSP 922 to apply filtering and/orprocessing on the signal across all frequency bands.

In one example, after full band processing by full band DSP 922,frequency domain processing 920 can split the signals into differentbands, applying variable gains to the different bands. The gain to eachband can be separately controlled to allow different gains for differentbands. System 900 illustrates the different band processing as band DSP930[1:N], collectively band DSPs 930. System 900 can apply variable gain932[1:N] (collectively variable gains 932), respectively, to band DSP930[1:N] prior to the band DSP. System 900 can apply variable gain934[1:N] (collectively variable gains 934), collectively, to band DSP930[1:N] after band DSP.

Separating the input signals into different frequency bands allows thesystem to reduce the power consumption for processing, circuit area, andsystem cost (operating cost as well as component cost) by processing onsignals in lower dynamic ranges. By separating the signals intodifferent bands, each band can be processed at a lower dynamic range,while preserving the overall large dynamic range of the entire frequencyband. The splitting into different bands can allow processing onsignificantly limited dynamic ranges, then recombining restores thedynamic range of the signal for further processing. The processing onthe entire band can be simpler because of the processing performed perband, thus minimizing the processing needed on a signal of large dynamicrange.

Digital frequency (FRED) domain AGC 936 can control the application ofvariable gains 932 and the application of variable gains 934. In oneexample, variable gains 932 apply signal gain or signal attenuation toprocess a signal with band DSPs 930, and then variable gains 934 providegain normalization to return the separate bands to a normalized rangefor recombining after processing. In one example, during thenormalization, any other variable gains applied by optical, analog, ortime domain AGC can also be normalized. The normalization can beperformed, for example, by padding bits in the MSBs or LSBs, dependingon the gain applied, to have signals with information bits aligned tothe proper bit range.

After recombining the full band signal, system 900 can apply additionalfull band DSP 924 to complete the frequency domain processing 920.Frequency domain processing 920 can send its signal output to peaksearch 950 for peak processing to generate detections 952. It should benoted that, according to some embodiments, frequency domain processing920 can be performed serially using one band DSP and one set of variablegain components and thus not limited to the depiction in FIG. 9 .

FIG. 10 illustrates an example LIDAR system that can implement AGC asdescribed herein. LIDAR system 1000 includes one or more of each of anumber of components, but may include fewer or additional componentsthan what is illustrated. One or more of the components depicted inLIDAR system 1000 can be implemented on a photonics chip, according tosome examples.

As shown, LIDAR system 1000 includes optical circuits 1012 implementedon a photonics chip. In one example, optical circuits 1012 includeactive optical components. In one example, optical circuits includepassive optical components. In one example, optical circuits 1012include a combination of active optical components and passive opticalcomponents. Active optical components refer to components that cangenerate, amplify, or detect optical signals, or perform a combinationof generate, amplify, or detect. In some examples, the active opticalcomponent performs operations on optical beams at different wavelengths,and includes one or more optical amplifiers, one or more opticaldetectors, or other components to perform operations on the lightsignal.

Free space optics 1032 refers to one or more components that can carryoptical signals and route and manipulate optical signals betweenappropriate input or output ports of the optical circuit and thecomponents of the optical circuit. In one example, free space optics1032 includes one or more optical components such as taps, wavelengthdivision multiplexers (WDM), splitters/combiners, polarization beamsplitters (PBS), collimators, couplers, or other components to direct anoptical signal. In some examples, free space optics 1032 includescomponents to transform the polarization state and direct receivedpolarized light, for example, to optical detectors using a PBS. In oneexample, free space optics 1032 includes a diffractive element todeflect optical beams having different frequencies at different anglesalong an axis (e.g., a fast axis).

In some examples, LIDAR system 1000 includes optical scanner 1042 thatincludes one or more scanning mirrors that are rotatable along an axis(e.g., a slow axis) that is orthogonal or substantially orthogonal tothe fast axis of the diffractive element. Optical scanner 1042 can steeroptical signals to scan an environment according to a scanning pattern.For instance, the scanning mirrors can be rotatable by one or moregalvanometers. Incident light from a source optical signal tends toscatter off objects in a target environment, generating a return opticalbeam or a target return signal. Optical scanner 1042 can collect thereturn optical beam or the target return signal and provide the returnsignal for processing. Optical scanner 1042 can return the signal topassive optical circuit components or active optical circuit componentsof optical circuits 1012. For example, free space optics 1032 can directa signal to an optical detector via a polarization beam splitter. Inaddition to mirrors and galvanometers, examples of optical scanner 1042can include components such as a quarter-wave plate, lens,anti-reflective coated window, or other component to receive an opticalsignal.

To control and support optical circuits 1012 and optical scanner 1042,LIDAR system 1000 includes LIDAR control system 1020. LIDAR controlsystem 1020 includes a signal processor, control component, or otherdevice to process control operations for LIDAR system 1000. The signalprocessor represents a processing device to control the operation ofLIDAR system 1000. The signal processor can be or include, for example,one or more general-purpose processing devices such as a microprocessor,central processing unit, processing component, or othercontroller/processor. The signal processor can be, for example, acomplex instruction set computing (CISC) microprocessor, a reducedinstruction set computer (RISC) microprocessor, a very long instructionword (VLIW) microprocessor, or a processor implementing otherinstruction sets, or processors implementing a combination ofinstruction sets. In one example, the signal processor can be or includeone or more special-purpose processing devices such as an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA), a digital signal processor (DSP), network processor, or othercomputation component.

In some examples, LIDAR control system 1020 includes signal processingunit 1022. Signal processing unit 1022 represents a processing devicespecific for perform signal computations. For example, signal processingunit 1022 can be a DSP. LIDAR control system 1020 can be configured tooutput digital control signals to control optical drivers 1014. In someexamples, the digital control signals can be converted to analog signalsthrough signal conversion unit 1016. For example, signal conversion unit1016 can include a digital-to-analog converter (DAC). Optical drivers1014 can provide drive signals to active optical components of opticalcircuits 1012 to drive optical sources such as lasers and amplifiers. Insome examples, several optical drivers 1014 and signal conversion units1016 can be provided to drive multiple optical sources.

LIDAR control system 1020 can be configured to output digital controlsignals for optical scanner 1042. Motion control system 1050 can controlgalvanometers or other movable components of optical scanner 1042 basedon control signals received from LIDAR control system 1020. For example,a DAC can convert coordinate routing information from LIDAR controlsystem 1020 to signals interpretable by galvanometers in optical scanner1042. In some examples, motion control system 1050 can returninformation to LIDAR control system 1020 about the position or operationof components of optical scanner 1042. For example, an analog-to-digitalconverter (ADC) can convert information about a galvanometer's positionto a signal interpretable by LIDAR control system 1020.

LIDAR control system 1020 can be configured to analyze incoming digitalsignals. In this regard, LIDAR system 1000 includes free opticalreceivers 1034 to measure one or more beams received by free spaceoptics 1032, which can also be passed to optical circuits 1012. Forexample, a reference beam receiver can measure the amplitude of areference beam from an active optical component, and an ADC convertssignals from the reference receiver to signals interpretable by LIDARcontrol system 1020. Target receivers measure the optical signal thatcarries information about the range and velocity of a target in the formof a beat frequency, modulated optical signal. The reflected beam can bemixed with a signal from a local oscillator. Optical receivers 1034 caninclude a high-speed ADC to convert signals from the target receiver tosignals interpretable by LIDAR control system 1020. In some examples,signal conditioning unit 1036 can perform signal conditioning on signalsfrom optical receivers 1034 prior to receipt by LIDAR control system1020. For example, the signals from optical receivers 1034 can beprovided to an operational amplifier (op-amp) for amplification of thereturn signals and the amplified signals can be provided to LIDARcontrol system 1020.

In some applications, LIDAR system 1000 includes one or more imagingdevices 1060 configured to capture images of the environment, globalpositioning system (GPS) 1080 configured to provide a geographiclocation of the system, or other sensor inputs. Image processing system1070 represents one or more components configured to receive the imagesfrom imaging devices 1060 or geographic location from GPS 1080 andprepare the information for receipt and use by LIDAR control system 1020or other system connected to LIDAR system 1000. For example, imageinformation can be pre-processed for use by LIDAR control system 1020.In another example, location information can be formatted for use byLIDAR system 1000.

In some examples, the scanning process begins with optical drivers 1014and LIDAR control system 1020. LIDAR control system 1020 can instructoptical drivers 1014 to independently modulate one or more opticalbeams, and these modulated signals propagate through the optical circuitto a collimator. The collimator directs the light at the opticalscanning system that scans the environment over a preprogrammed patterndefined by motion control system 1050. Optical circuits 1012 can includea polarization wave plate (PWP) to transform the polarization of thelight as it leaves optical circuits 1012. In some examples, thepolarization wave plate can be a quarter-wave plate or a half-waveplate. A portion of the polarized light can be reflected back to opticalcircuits 1012. For example, lensing or collimating systems used in LIDARsystem 1000 can have natural reflective properties or a reflectivecoating to reflect a portion of the light back to optical circuits 1012.

Optical signals reflected back from the environment pass through opticalcircuits 1012 to the receivers. If the polarization of the light hasbeen transformed, it can be reflected by a polarization beam splitter(PBS) along with the portion of polarized light that was reflected backto optical circuits 1012. Accordingly, rather than returning to the samefiber or waveguide as an optical source, the reflected light can bereflected to separate optical receivers. These signals interfere withone another and generate a combined signal. Each beam signal thatreturns from the target produces a time-shifted waveform. The temporalphase difference between the two waveforms generates a beat frequencymeasured on the optical receivers (photodetectors). The combined signalcan then be reflected to optical receivers 1034.

Optical receivers 1034 can apply ADCs to convert the analog signals fromoptical receivers to digital signals. The digital signals are then sentto LIDAR control system 1020. Signal processing unit 1022 can receivethe digital signals and interpret them. In some examples, signalprocessing unit 1022 also receives position data from motion controlsystem 1050 and galvanometers (not shown) as well as image data fromimage processing system 1070. Signal processing unit 1022 can thengenerate a 3D point cloud with information about range and velocity ofpoints in the environment as optical scanner 1042 scans additionalpoints. Signal processing unit 1022 can also overlay a 3D point clouddata with the image data to determine velocity and distance of objectsin the surrounding area. In one example, LIDAR system 1000 processessatellite-based navigation location data to provide a precise globallocation.

In operation according to some examples, LIDAR system 1000 can beconfigured to provide AGC. The AGC can be applied anywhere in the signalpath, in accordance with any example provided. In one example, the AGCcan be applied to an optical signal in an optical time domain signalpath. In one example, the AGC can be applied to an electrical signal inan analog time domain signal path. In one example, the AGC can beapplied to a digital signal in a time domain signal path. In oneexample, the AGC can be applied to a digital signal in a frequencydomain signal path. AGC can be applied at more than one location in asignal path.

FIG. 11 represents a time-frequency diagram illustrating an example ofLIDAR waveform detection and processing. Diagram 1100 represents atime-frequency diagram of an FMCW scanning signal 1110 that can be usedby a LIDAR system in accordance with embodiments of the presentdisclosure to scan a target environment according to some examples. Inone example, the scanning waveform 1110, labeled as f_(FM)(t), can be asawtooth waveform (sawtooth “chirp”) with a chirp bandwidth Δf_(C) and achirp period T_(C).

The slope of the sawtooth is given as k=(Δf_(C)/T_(C)). Diagram 1100also depicts target return signal 1120 according to some examples.Target return signal 1120, labeled as f_(FM)(t−Δt), is a time-delayedversion of scanning signal 1110, where Δt is the roundtrip time to andfrom a target illuminated by scanning signal 1110. The roundtrip timecan be given as Δt=11R/v, where R is the target range, and v is thevelocity of the optical beam, which can be the speed of light c. Thetarget range, R, can therefore be calculated as R=c(Δt/2).

When return signal 1120 is optically mixed with scanning signal 1110, arange-dependent difference frequency, referred to as the beat frequency,Δf_(R)(t) can be generated. The beat frequency Δf_(R)(t) can be linearlyrelated to the time delay, Δt, by the slope of the sawtooth k. Thus,Δf_(R)(t)=kΔt. Since the target range R is proportional to Δt, thetarget range R can be calculated as R=(c/2)(Δf_(R)(t)/k). Thus, therange R is linearly related to the beat frequency Δf_(R)(t).

The beat frequency Δf_(R)(t) can be generated, for example, as an analogsignal in optical receivers 1034 of system 1000. The beat frequency canthen be digitized by an ADC, for example, in a signal conditioning unitsuch as signal conditioning unit 1036 in LIDAR system 1000. Thedigitized beat frequency signal can then be digitally processed, forexample, in a signal processing unit, such as signal processing unit1022 in system 1000.

It will be understood that target return signal 1120 will, in general,also include a frequency offset (Doppler shift) if the target has avelocity relative to the LIDAR system. The Doppler shift can bedetermined separately, and used to correct the frequency of the returnsignal, so the Doppler shift is not shown in diagram 1100 for simplicityand ease of explanation. It should also be noted that the samplingfrequency of the ADC will determine the highest beat frequency that canbe processed by the system without aliasing. In general, the highestfrequency that can be processed is one-half of the sampling frequency(i.e., the “Nyquist limit”).

In one example, and without limitation, if the sampling frequency of theADC is 1 gigahertz, then the highest beat frequency that can beprocessed without aliasing (Δf_(Rmax)) is 500 megahertz. This limit inturn determines the maximum range of the system asRmax=(c/2)(Δf_(Rmax)/k) which can be adjusted by changing the chirpslope k. In one example, while the data samples from the ADC may becontinuous, the subsequent digital processing described below may bepartitioned into “time segments” that can be associated with someperiodicity in the LIDAR system. In one example, and without limitation,a time segment might correspond to a predetermined number of chirpperiods T, or a number of full rotations in azimuth by the opticalscanner.

FIG. 12 illustrates an example of a LIDAR system that provides AGC for aLIDAR signal. System 1200 represents a system in accordance withembodiments of the present disclosure. System 1200 includes LIDAR 1210,which represents a LIDAR system in accordance with any example herein.

In one example, LIDAR 1210 represents an optical chip, which can becoupled to a processor device or processor chip and a memory device ormemory chip. In one example, system 1200 can be a single device withLIDAR, processing, and memory components in a single device or devicepackage. In one example, LIDAR 1210 can be one of multiple LIDARcomponents coupled to a processing device.

LIDAR 1210 includes laser 1220 to provide an optical signal. Opticalcircuit 1230 includes one or more optical circuit components or elementsto provide modulation, reference signaling, optical combining or otheroptical manipulation of an optical signal, amplification or attenuation,or other operation on an optical signal for system 1200. The modulationcan be active or passive. Optical circuit 1730 provides the modulationand optics to transmit TX signal 1222 to target 1240 and receive thereflection signal represented by RX signal 1242.

Photodetector 1250 can receive RX signal 1242 from optical circuit 1230from target 1240, and LO signal 1224 from optical circuit 1230 fromlaser 1220. System 1200 can condition the signal with one or morecircuit components, represented by circuit 1260. In one example, circuit1260 includes an ADC component. Circuit 1260 can condition the receivedsignal detected by photodetector 1250.

Processor 1270 represents a processor device or processing unit.Processor 1270 can be a standalone component or be integrated in acomputer system. Processor 1270 can provide time domain and frequencydomain processing. Processor 1270 can compute or determine a targetrange value for target 1240 and/or a target velocity value for target1240 based on the optical signal scanning and detected reflectionsignals.

The values generated can be part of a point cloud of information to mapan environment of target 1240. In one example, system 1200 includesmemory 1280 coupled to processor 1270 to store information computed byprocessor 1270, and to provide data for computation by processor 1270.In one example, memory 1280 stores point cloud 1282, to represent theinformation gathered by scanning target 1240 with LIDAR 1210. Pointcloud 1282 can be or include estimates or values computed by processor1270 based on scanning target 1240.

In one example, system 1200 includes AGC. Various AGC elements arerepresented in system 1200. In one example, system 1200 includes morethan one of an optical AGC at LO path 1226, an analog AGC at path 1252,a time domain AGC (one example of AGC 1272 in processor 1270), or afrequency domain AGC (another example of AGC 1272 in processor 1270).

In one example, system 1200 includes an AGC at LO path 1226. Such an AGCcan be referred to as an optical AGC, to provide variable gain to alight signal. The variable gain can increase the gain when the signal islower than a threshold, and the variable gain can attenuate the signalto fit within a smaller dynamic range of subsequent processing elements.In one example, system 1200 includes an AGC at path 1252, betweenphotodetector 1250 and circuit 1260. In one example, the AGC can beconsidered part of circuit 1260. The AGC at path 1252 can be referred toas an analog AGC. The analog AGC can provide variable gain to anelectrical signal generated from a detected return beam. The variablegain can increase the gain when the signal is lower than a threshold,and the variable gain can attenuate the signal to fit within a smallerdynamic range of subsequent processing elements.

In one example, processor 1270 includes AGC 1272. In one example, AGC1272 can represent a time domain AGC or digital time domain AGC in adigital processing path of the signal received from LIDAR 1210. Thedigital time domain AGC can provide variable gain to a digital signalwithin processor 1270. The variable gain can increase the gain when thesignal is lower than a threshold, and the variable gain can attenuatethe signal to fit within a smaller dynamic range for subsequentprocessing.

In one example, AGC 1272 can represent a frequency domain AGC or digitalfrequency domain AGC in a digital processing path of the signal receivedfrom LIDAR 1210. The digital frequency domain AGC can provide variablegain to a frequency signal within processor 1270. The variable gain canincrease the gain when the signal is lower than a threshold, and thevariable gain can attenuate the signal to fit within a smaller dynamicrange for subsequent processing.

Besides what is described herein, various modifications can be made tothe disclosed embodiments and implementations of the invention withoutdeparting from their scope. Therefore, the illustrations and examplesherein should be construed in an illustrative, and not a restrictivesense.

What is claimed is:
 1. A light detection and ranging (LIDAR) system,comprising: an optical source to transmit a first portion of a lightsignal toward a target; a photodetector to detect the light signal as areturn beam from the target, the light signal having a first dynamicrange in a time domain of the LIDAR system; an analog to digitalconverter (ADC) to generate a digital signal based on the return beamdetected at the photodetector; a processor, coupled to thephotodetector, to: perform time domain processing on the digital signalin the time domain; convert the digital signal from the time domain to afrequency domain; and perform frequency domain processing on the digitalsignal in the frequency domain; and an automatic gain control (AGC) unitto: measure a power of the digital signal in the frequency domain; andapply variable gain to the digital signal in the frequency domain toreduce the dynamic range to a second dynamic range lower than the firstdynamic range prior to further processing by the processor.
 2. The LIDARsystem of claim 1, wherein the AGC unit comprises a digital AGC unit inthe processor, wherein the digital AGC unit is to: measure an inputpower of the digital signal within a specific frequency band; determinea desired dynamic range of the digital signal; and adjust the digitalsignal with variable gain to be within the desired dynamic range.
 3. TheLIDAR system of claim 2, wherein the digital signal has an associatednumber of bits, and wherein the AGC unit is to: determine if the digitalsignal has a signal level above an AGC threshold; provided the AGCthreshold is exceeded, select a subset of the associated number of bits;and perform processing on the subset of the associated number of bits.4. The LIDAR system of claim 3, wherein the digital signal has anassociated number of bits, and wherein the digital AGC unit is to:compare a signal level of the digital signal to a threshold to dividethe first dynamic range into multiple reduced ranges; and provided thedigital signal is above the threshold, select a subset of the number ofbits based on which of the multiple reduced ranges the digital signalbelongs to; and perform processing on the subset of the number of bits.5. The LIDAR system of claim 4, wherein the digital AGC unit is tocompare the signal level to multiple thresholds to divide the dynamicrange into the multiple reduced ranges.
 6. The LIDAR system of claim 2,wherein the AGC unit is to: separate the digital signal into differentfrequency bands; and apply different variable gains to portions of thesignal in different frequency bands.
 7. The LIDAR system of claim 6,wherein the AGC unit is to: normalize the portions of the signal fromthe different frequency bands after application of the differentvariable gains; and combine the portions of the signal from thedifferent frequency bands into a composite signal.
 8. The LIDAR systemof claim 6, wherein the AGC unit is to: separate the digital signal intothe different frequency bands to apply processing on separate bands atthe second dynamic range; and recombine the separate bands into a fullband signal having the first dynamic range.
 9. A method for a lightdetection and ranging (LIDAR) system, comprising: transmitting a firstportion of a light signal toward a target; detecting the light signal asa return beam from the target at a photodetector, the light signalhaving a first dynamic range in a time domain of the LIDAR system;generating a digital signal based on the return beam detected at thephotodetector; performing time domain processing on the digital signalin the time domain; converting the digital signal from the time domainto a frequency domain; and performing frequency domain processing on thedigital signal in the frequency domain; measuring a power of the digitalsignal in the frequency domain; and applying variable gain to thedigital signal in the frequency domain to reduce the dynamic range to asecond dynamic range lower than the first dynamic range.
 10. The methodof claim 9, wherein measuring the power of the digital signal comprisesmeasuring an input power of the digital signal within a specificfrequency band, and wherein applying the variable gain comprises:determining a desired dynamic range of the digital signal; and adjustingthe digital signal with variable gain to be within the desired dynamicrange.
 11. The method of claim 10, wherein the digital signal has anassociated number of bits, and further comprising: determining if thedigital signal has a signal level above an AGC threshold; provided theAGC threshold is exceeded, selecting a subset of the associated numberof bits; and applying the variable gain by performing processing on thesubset of the associated number of bits.
 12. The method of claim 11,wherein selecting the subset of the associated number of bits comprises:comparing a signal level of the digital signal to a threshold to dividethe first dynamic range into multiple reduced ranges; and provided thedigital signal is above the threshold, selecting a subset of the numberof bits based on which of the multiple reduced ranges the digital signalbelongs to.
 13. The method of claim 12, wherein comparing the signallevel to the threshold comprises comparing the signal level to multiplethresholds to divide the dynamic range into the multiple reduced ranges.14. The method of claim 9, further comprising: separating the digitalsignal into different frequency bands; and applying different variablegains to portions of the signal in different frequency bands.
 15. Themethod of claim 14, further comprising: normalizing the portions of thesignal from the different frequency bands after application of thedifferent variable gains; and combining the portions of the signal fromthe different frequency bands into a composite signal.
 16. The method ofclaim 14, wherein applying the different variable gains comprises:applying processing on separate bands at the second dynamic rangerecombining the separate bands into a full band signal having the firstdynamic range.
 17. A light detection and ranging (LIDAR) system,comprising: a light source to transmit a light signal toward a target;an optical circuit including: a photodetector to detect the light signalas a return beam from the target, the return beam having a first dynamicrange in a time domain of the LIDAR system; an analog to digitalconverter (ADC) to generate a digital signal based on the return beamdetected at the photodetector; a processing device coupled to thephotodetector, to: convert the digital signal from the time domain to afrequency domain; and perform frequency domain processing on the digitalsignal in the frequency domain; and an automatic gain control (AGC) unitto: measure a power of the digital signal in the frequency domain; andapply variable gain to the digital signal in the frequency domain toreduce the dynamic range to a second dynamic range lower than the firstdynamic range prior to further processing; and optics to direct thesignal from the light source toward the target and direct the returnbeam to the photodetector.
 18. The LIDAR system of claim 17, wherein theAGC unit comprises a digital AGC unit in the processing device, whereinthe digital AGC unit is to: measure an input power of the digital signalwithin a specific frequency band; determine a desired dynamic range ofthe digital signal; and adjust the digital signal with variable gain tobe within the desired dynamic range.
 19. The LIDAR system of claim 18,wherein the digital signal has an associated number of bits, and whereinthe AGC unit is to: compare a signal level of the digital signal to athreshold to divide the first dynamic range into multiple reducedranges; and provided the digital signal is above the threshold, select asubset of the number of bits based on which of the multiple reducedranges the digital signal belongs to; and perform processing on thesubset of the number of bits.
 20. The LIDAR system of claim 18, whereinthe AGC unit is to: separate the digital signal into different frequencybands; apply different variable gains to portions of the signal indifferent frequency bands at the second dynamic range; and recombine thedifferent frequency bands into a full band signal having the firstdynamic range.